The present invention relates to surgery performed by local heating guided by magnetic resonance (MR) imaging, and more particularly to a method and apparatus for performing surgery by pulsed local heating guided by real-time temperature-sensitive MR imaging.
Conventional MR imaging provides an operator, such as a surgeon or a radiologist, with internal views of a patient's anatomy. MR imaging provides excellent contrast between different tissues and is useful in planning surgical procedures. Many tissues in a patient such as a tumor, are much more visible in an MR image than as seen in actual surgery. The tumor can also be obscured by blood during surgery further reducing visibility.
Experiments on living tissue show that a heated zone above a critical temperature destroys tissue. This zone increases in size with time as the heat is applied to reach a steady state of both temperature and heat flow. If the maximum temperature is limited, then an area heated to a temperature exceeding the critical temperature causing destruction of tissue, approaches a predetermined size.
Researchers at Brigham and Womens Hospital, Boston, Mass. have proposed treatment of deep lying tumors by laser surgery, as described in "MR Imaging of Laser-Tissue Interactions", by F. A. Jolesz, A. R. Bleire, P. Jakob, P. W. Ruenzel, K. Huttl, G. J. Jako, Radiology 168:249 (1989).
In laser surgery of the brain, a small burr hole is drilled in the skull and a hollow needle containing an optical fiber is then inserted into the tumor. Optical energy is passed through the optical fiber and into the tumor heating the tumor. Lasers guided through fiber optics are potentially very useful for surgery in the brain, since they allow access (through biopsy needles) to deeply buried pathology with minimal disruption of intervening tissue. The laser destroys the pathological tissue through localized heating.
A view of the heated region is provided with the use of MR temperature-sensitive pulse sequences. One known MR temperature-sensitive pulse sequence is described in U.S. Pat. No. 4,914,608 "In-vivo Method for Determining and Imaging Temperature of an Object/Patient from Diffusion Coefficients Obtained by Nuclear Magnetic Resonance", by Denis LeBihan, Jose Delannoy, and Ronald L. Levin issued Apr. 3, 1990. This sequence causes full MR images to be created. It is, therefore, relatively slow, time-consuming and not capable of monitoring quickly changing temperatures.
In focussed ultrasound surgery, acoustic energy is concentrated at a focal point within the tumor. The focussed acoustic energy causes heating of tissue at the focal point.
Tumors have been selectively destroyed in cancer patients using focussed ultrasound to heat tissue within the patient at the University of Arizona as reported in "Effects of Physical Parameters on High Temperature Ultrasound Hyperthermia" by B. E. Billard, K. Hynynen and Robert. B. Roemer, Ultrasound in Med. & Biol. Vol. 16, No. 4, pp. 409-420, 1990. Billard et al. disclose that the control of heat is improved by using short heating pulses where the effect of blood perfusion is negligible. However, since they do not image the temperature distribution, it is difficult to hit small, deep laying targets.
It would be beneficial to accurately image, in real time, localized heating and selectively destroy a specific tissue with minimal invasiveness without harming surrounding healthy tissue.